Hard disc drive (HDD) and other data storage device access systems often use port multipliers to interface between host devices and multiple data storage devices. For example, SATA (Serial Advanced Technology Attachment) port multipliers are often connected between a single host port and data storage devices and often have support for up to fifteen (15) different endpoint data storage devices. The resulting data storage network increases both storage capacity and host utilization but also requires system level power management to be provided for the attached data storage devices.
A Host-on-Demand (HOD) algorithm is one power management scheme that is often used to manage power modes for data storage devices, such as HDD devices, attached to a SATA port multiplier. The HOD algorithm provides that the power state of a given storage device may change only when the host processes a command for that storage device. Because the changing of power states can take up to several seconds using the HOD power management algorithm, access latency can be significant when power up is required for data storage devices that are in low power modes when accessed. This access latency can cause poor communication bandwidth utilization that degrades overall performance. Alternatively, low power modes can be avoided to reduce or eliminate such power up delays and thereby avoid this access latency. However, this avoidance of low power modes can significantly reduce the amount of power that can be saved in operating the data storage devices. As such, power savings are often sacrificed to achieve reduced access latency when HOD power management algorithms are applied.